The present invention relates to a parking brake mechanism assembled within a hydraulic drum brake assembly for wheeled vehicles, and relates more particularly to a mechanical parking brake mechanism of the type which includes a parking lever assembled within such a hydraulic drum brake assembly as a leading-trailing type drum brake, a duo-servo type drum brake, or the like, the parking lever being arranged to cooperate with a strut of the drum brake assembly in such a way as to displace a pair of brake shoes outwardly toward the inner periphery of the brake drum.
In such a conventional parking brake mechanism as described above, a parking brake wire is connected to the free end of the parking lever and is guided at its intermediate portion by means of such a guide device as an anchor plate for the brake shoes, a bell-crank or a sector pulley pivoted to the backing plate of the brake drum, or the like. When an anchor plate is applied to guide the parking brake wire, frictional resistance at the guided portion of the parking brake wire results in a decrease in the transfer efficiency of the input force applied to the parking lever. In the case that the parking brake wire is guided by provision of a bell-crank, the lever ratio of the parking lever changes in accordance with the length of the pulling stroke of the parking brake wire. Furthermore, in the case that a sector pulley is applied to guide the parking brake wire, it is required to fix the intermediate portion of the parking brake wire to a portion of the guide face of the sector pulley by means of caulking. If the length of pulling stroke of the wire increases to produce an excessive force acting on the fixed portion of the wire, the wire will be disconnected at its fixed portion, resulting in a marked decrease in the transfer efficiency of the input force.